1. Field of the Invention
The invention relates to bipolar electrosurgical instruments and, more particularly, to bipolar instruments for selectively grasping, manipulating, cutting and/or coagulating body tissue.
2. Description of the Related Art
Electrosurgery involves the cutting and/or coagulating of body tissue by application of high frequency electrical current. In bipolar electrosurgery, the electrical current is applied through an electrode which contacts the body tissue to be treated. A return electrode is placed in contact with or in close proximity to the current-supplying electrode such that an electrical circuit is formed between the two electrodes. In this manner, the applied electrical current is limited to the body tissue positioned between the electrodes. When the electrodes are sufficiently separated from one another, the electrical circuit is open and thus inadvertent contact of body tissue with either of the separated electrodes does not cause current to flow.
To perform tissue cutting and/or coagulation, a high frequency power supply is connected to the bipolar instrument. Each electrode of the bipolar instrument is electrically isolated within the instrument and is separately connected to the high frequency power supply. Typical power supplies such as the SSE2L.TM. available from Valleylab, Inc. of Boulder, Colo., are r.f. generators which can produce different electrical waveforms to effect various electrosurgical procedures.
A waveform of continuous sinewaves alternating from positive to negative at the operating frequency of the r.f. generator is employed to cut tissue. Such a waveform creates short, intense electrical sparks to rapidly heat tissue; cells are exploded and the heat dissipated as steam.
A waveform consisting of pulsating sine waves alternating from positive to negative at the operating frequency of the r.f. generator is employed to coagulate tissue. Such a waveform creates longer, less intense sparks which heat tissue less rapidly, allowing heat to be dissipated more widely than during cutting. A combination of the cutting and coagulating waveforms produces the capability to cut tissue with enhanced hemostasis over the pure cutting waveform.
A fuller description concerning the electrical aspects of electrosurgery can be found in the Valleylab SSE2L.TM. Instruction Manual published by Valleylab of Boulder, Colo., the disclosure of which is incorporated herein by reference.
Electrosurgical procedures have, in recent years, become increasingly widespread. The ease and speed of cutting and/or coagulating tissue saves the surgeon valuable time while minimizing internal bleeding by the patient. Endoscopic and laparoscopic surgical procedures have created additional incentives for the use of electrosurgical techniques. In laparoscopic procedures, surgery is performed in the interior of the abdomen through a small incision; in endoscopic procedures, surgery is performed in any hollow viscus of the body through narrow tubes inserted through small entrance wounds in the skin. Because laparoscopic and endoscopic surgery do not bring the surgeon into direct contact with the operation site, internal bleeding must be quickly controlled by instruments easily operable from a remote location. Electrosurgical instruments provide the surgeon with the ability to electrically cut tissue such that bleeding is minimized and to effectively seal off bleeders during laparoscopic and endoscopic procedures.
Several configurations have been proposed for bipolar electrosurgical instruments particularly adapted for treating tissue. Bipolar knives are described in U.S. Pat. Nos. 4,161,950 and 4,232,676. In these patents, two or more separated, fixed electrodes are disposed on the surface of a ceramic blade. These electrodes are used to cut and/or coagulate tissue when electrical current passes through tissue positioned between a pair of these fixed electrodes.
Another bipolar electrosurgical instrument is the bipolar forceps. This instrument, examples of which are described in U.S. Pat. Nos. 3,643,663 and 4,003,380, is used to treat tissue held between the conductive forceps jaws. Current flows through tissue held between the forceps jaws to effect cutting and/or coagulation of the tissue.
Other designs for bipolar forceps have been proposed. In U.S. Pat. No. 5,151,102, a sintered, insulating blood vessel contact member is provided on stainless steel or titanium forceps. Exposed electrodes of a conductive resin are disposed over the surface of the vessel contact member.
The product literature for EVERS HEARS.RTM., available from Everest Medical Corporation, Minneapolis, Minn., describes laparoscopic scissors. Ceramic blades and a single-action dissecting tip are illustrated.
In all of the instruments described above, approximation of the jaws, or, in the case of bipolar knives and probes, the fixed relative position of the electrodes, creates an electrical circuit. As long as electrical current is supplied to the instrument and material capable of transporting the current, e.g., tissue, fluid, or ionized air, is positioned between the electrodes, current will flow and an electrical circuit will be maintained.
When both jaws are fabricated from electrically conductive material, as in the prior art, a bipolar electrosurgical instrument is not capable of automatic circuit interruption when the jaws are fully approximated. The user must either turn the instrument off or allow electrical treatment to proceed until tissue positioned between the jaws is no longer capable of conducting an electrical current.
Prior bipolar forceps, scissors, and the like additionally employ a substantial quantity of high thermal conductivity materials, such as metals, in jaw construction. The use of these materials causes the jaw members to heat substantially, even when portions of the jaws use insulating materials. This heating is undesirable in many surgical procedures.
A need exists in the art for bipolar electrosurgical instruments having jaw members employing minimal amounts of thermally conductive materials. A need also exists in the art for improved bipolar electrosurgical instruments in which an electrical circuit is formed as the instrument's jaws are approximated. Such instruments could be advantageously used to electrically treat tissue by cutting, coagulation, or a combination of cutting and coagulation.